1. Field of the Invention
The present invention relates generally to metal-to-metal seals and, more particularly, to a resilient metal-to-metal seal that in one embodiment may be mounted in a wellhead or BOP to control very high pressures, high temperature, and caustic fluids.
2. Description of the Prior Art
Metal-to-metal seals have advantages over non-metallic seals in that they operate over a wider range of temperatures, fluids, and pressures. Non-metallic seals of various materials are best matched to a particular range of temperatures, fluids, and pressures. Neither the operator nor the manufacturer will always know the conditions under which wellhead devices may be utilized, which increases the risk of failure.
In the past, metal-to-metal seals have often been made of soft metals that deform to create a one-time-use seal. One of the problems of soft metal seals is that all seals must be replaced whenever the wellhead device is opened. The deformed material is unlikely to seal again when used more than once. Another problem is that these types of seals do not always make an initial seal, thereby necessitating opening up the wellhead device and replacing that seal as well as all other metal seals.
To the extent that hard metal-to-metal seals are utilized in the prior art, fine tolerances are often required that essentially limit the pressure that can be sealed. Moreover, small variations in the tolerances can render the seal ineffective.
To the extent resilient metal seals have been utilized, they are subject to problems in obtaining an initial seal and/or maintaining a seal with over wide pressure variations.
The following U.S. patents describe various prior art efforts related to making metal-to-metal seals:
U.S. Pat. No. 4,911,245, issued Mar. 27, 1990, to Adamek et al, discloses a metal seal for sealing against casing in a well with a plurality of circumferentially axially spaced metal bands. An inlay material partially fills the cavities located between the metal bands. The metal bands are soft enough to deform when the seal is pressed into contact with the casing. The bands deform to a point flush with the inlay material. If the casing later moves axially relative to the seal because of temperature change or tension loading, then the inlay material will wipe across the band faces to maintain the seal.
U.S. Pat. No. 5,257,792, issued Nov. 2, 1993, to Putch et al, discloses a metal well head seal for sealing between inner and outer concentric well head components which includes a circular metal seal having a flat end and a tapered end and positioned between the inner and outer components. A forcing cone on one of the components engages the tapered end for sealing, a backup shoulder engages the flat end as the inner and outer components are longitudinally moved together for setting the metal seal. An adjusting nut adjusts the tolerances between the tapered end and the forcing cone.
U.S. Pat. No. 4,771,832, issued Sep. 20, 1988, to Bridges, discloses a wellhead assembly with a metal seal that accommodates misalignment between casing and the bore of the wellhead housing. The metal seal assembly includes a metal seal ring and a wedge ring. The seal ring has a cylindrical inner wall and a conical outer wall. The centerlines of the inner and outer walls are offset with respect to each other, making the ring eccentric. Similarly, the wedge ring has a conical inner wall and an outer wall. Its inner and outer walls are offset with respect to each other. The rings can be rotated relative to each other and to the casing to coincide the axis of the outer wall of the wedge ring with the axis of the wellhead housing bore. The inner wall of the seal ring has protruding bands which deform as a result of the softness of the metal to enhance sealing.
U.S. Pat. No. 3,166,345, issued Jan. 19, 1965, to Pinkard, discloses an improved sealing means including a seal ring, sealing between the cylindrical, upwardly extending neck of a tubing hanger element positioned in a tubing head, and a recess or socket of a bonnet flange, which is positioned over the upwardly extending cylindrical neck of the tubing hanger.
U.S. Pat. No. 4,455,040, issued Jun. 19, 1984, to Shinn, discloses a tubing head, tubing head adapter and tubing hanger sealed against annulus fluid or downhole pressure by an upper and a lower, pressure-energizing sealing assembly. The sealing assemblies are bi-directional, pressure-energizing and operate under working pressures of up to 30,000 psi. Each assembly consists of a metal seal ring made of highly elastic and ductile 316 stainless steel with a yield strength of approximately 30,000 psi, having a frustoconical shape, with the upper and lower tips of the cone enclosing an angle of approximately 28.degree. in the prestressed state. In the axial direction, the seal ring engages a support ring on one end and a tubing hanger shoulder at the other end, both of which form inclines of 30 degrees with the vertical (radial) plane. The support ring and the tubing hanger shoulders are made of materials having yield strengths of 50,000 psi and 75,000 psi, respectively. The preload applied to the seal assemblies is such that the seal ring plastically conforms to the harder surrounding surfaces and assumes a cone taper angle of 30 degree, in conformity with the mating support ring and tubing hanger shoulder. Thereafter, working pressure applied from either axial direction will be resolved along the incline of interacting surfaces into radial components which further enhance the sealing pressure along the inner and outer sealing surfaces. Because of this bidirectional pressure-enhancement, both seal assemblies may be tested through the application of test pressure from one common test port located between the two assemblies.
U.S. Pat. No. 4,056,272, issued Nov. 1, 1977, to Morrill, discloses an oil well pipe suspension apparatus including a wellhead having a pipe hanger supported therein and a Christmas tree supported thereon, a frusto-conical metal gasket providing a metal-to-metal seal between the hanger and the wellhead, and an “X” cross section resilient metal gasket providing a metal-to-metal seal between the hanger and the Christmas tree.
U.S. Patent Application No. 20050082829, published Apr. 21, 2005, to Dallas, discloses a metal ring gasket for a threaded union with a high-pressure, fluid-tight, metal-to-metal seal between subcomponents of a fluid conduit. The metal ring gasket is made of carbon steel or stainless steel depending on a composition of the fluid to be conveyed through the conduit. The metal ring gasket has beveled corners and is received in a beveled annular groove on mating surfaces of the subcomponents of the threaded union. When compressed in the annular groove between the subcomponents, the metal ring gasket creates an energized, high-pressure, fluid-tight seal that is highly resistant to pressure and is capable of maintaining a seal even at elevated temperatures resulting from direct exposure of the fluid conduit to fire.
U.S. Pat. No. 4,190,270, issued Feb. 26, 1980, to Vanderford, discloses a hanger for supporting tubing in a well head including a tubular body adapted for connection to a casing head and having a tapered and upwardly facing seat, a tubular hanger positioned within the body and supported on the seat, a downwardly converging annular space between facing portions on the exterior of the hanger and on the interior of the body, a metal seal ring positioned within the converging space, a seal actuator sleeve positioned between the hanger and the body and being movable axially to engage the seal ring, and a wedging screw extending through the body. The wedging screw engages the seal actuator sleeve and wedges the seal actuator sleeve onto the seal whereby the seal is forced into sealing engagement in the converging space between the hanger and the body.
U.S. Pat. No. 3,104,121, issued Sep. 17, 1963, to Nordin et al, discloses a seal assembly designed to withstand pressures such as those encountered at high pressure well heads which may be in the order of 20,000 p.s.i. A high pressure seal assembly for a flow control device, wherein the assembly includes co-acting surfaces between the flow control device and the main body for accommodating a seal structure to provide an improved seal equally effective against pressure applied from either direction.
U.S. Pat. No. 3,494,638, issued Feb. 10, 1970, to Todd et al, discloses a tubing hanger assembly including an adapter and seal assembly, mounted between the tubing head and the valve fitting at the top of a well, with the seal assembly being mounted in the bore of the adapter body, and held therein by a removable retaining nut and with the addition of a liquid seal injection valve communicating with the seal therein and a test port through the wall of the adapter for receiving a gauge for testing the seal prior to installing the adapter on the tubing head.
The solutions to the above described and/or related problems have been long sought without success. Consequently, those of skill in the art will appreciate the present invention, which addresses the above problems and other significant problems uncovered by the inventor that are discussed hereinafter.